In a semiconductor element, low-resistance contact between an n-type semiconductor region and metal is needed. Similarly, low-resistance contact between a p-type semiconductor region and metal is needed. In a semiconductor element based on, for example, silicon (Si), the sum of barrier between an n-type region or p-type region and a metal for the same metal is about 1 eV of the magnitude of a bandgap. In this case, a sufficiently low contact resistance can be obtained by sufficiently increasing the amount of dopant in both regions. That is, the barrier can be set sufficiently low and a sufficient amount of dopant can be introduced for activation and thus, forming simultaneous contact to both the n-type semiconductor region and the p-type semiconductor region does not pose a big problem.
In a silicon carbide (SiC) power semiconductor device, however, the sum of barrier between an n-type semiconductor region or p-type semiconductor region and a metal for the same metal amounts to about 3 eV of the magnitude of a bandgap. Thus, for use of the semiconductor device as a product, steps are needed such as using different metals for electrodes between the n-type region and the p-type region to reduce the resistance. It is also necessary to introduce the dopant in higher concentrations to reduce the resistance and further, a long-term high-temperature process is needed for activation. An interface between, for example, an SiC semiconductor and a dielectric film is caused to deteriorate by the high-temperature process. Thus, it is desirable to reduce the resistance at a lower temperature.
Regarding contact between, for example, a large n-type SiC region and metal, a satisfactory value to some extent is obtained for a reduction of resistance by using an interface reaction layer in a high-temperature process. Regarding contact between a p-type SiC region and metal, however, an obtained value cannot be said to be entirely satisfactory even for a large region. This stems from material characteristics of the material SiC. That is, the material itself has a large bandgap. This is an intrinsic problem of a wide bandgap semiconductor because any electrode capable of making low-resistance contact with an n-type SiC region has a barrier to a p-type SiC region as large as the bandgap.
As described above, for low-resistance contact between an n-type SiC region and metal, there is a problem that a high-temperature process is needed. For low-resistance contact between a p-type SiC region and metal, there is a problem that even realization thereof is insufficient with the same metal as that of the n-type SiC region. Thus, there is a problem that the type of metal to be used is sharply restricted.